Waste oils, especially used lubricating oils (ULO), are considered a threat to the environment, and is classified as a hazardous product in most jurisdictions. The Environment Protection Agency (EPA) states that: “One gallon of used lubricating oil can pollute a million gallons of water.” There is a need for a viable and flexible process that can destroy the hazardous components of ULO and produce useful products with little or no by-products to dispose of in industrial landfills or incinerators.
There are many processes to treat waste oils. Up until the December 2001 report to the European Commission of the Environment by Taylor Nelson Sofres titled “Critical review of existing studies and life cycle analysis on the regeneration and incineration of waste oils”, and the Nov. 19, 2008 European union directive, there was priority given to re-refining processes recycling waste oils into lubricating oils in the European Union as well as in the rest of the World. Consequently many re-refining processes were invented and used. The commercial re-refining processes used in Europe are described in the Taylor Nelson Sofres report. These and others are described in a book by Francois Audibert titled “Waste Engine Oils, Re-refining and Energy Recovery”, (Elsevier, Amsterdam, 2006). Among the processes that regenerate ULO into lubricating oil base-stocks, some, such as the acid clay processes, were abandoned or legislated out because of the disposal costs, both financial and environmental, of the by-products such as spent acid and clays.
Lube oil regeneration processes, using solvent extraction or vacuum distillation as their primary process, require a finishing step, such as hydrotreating, which entails the purchase of hydrogen or building a hydrogen unit. Usually, the quality of their feedstock determines the quality of their products. Waste oil compositions are variable, and can change even within a shipment. Re-refining processes usually require extensive laboratory analyses of both the waste oil entering the plant, to determine the amount of chemicals to add in their pre-treatment processes, and of the product lubricating oils to ensure consistent product quality. Because of their high capital and operating costs, these plants must be close to large population centre and/or serve a large collection area, and usually require government subsidies to be viable.
When the used oil is to be used as fuel, chemical treatment of ULO to extract heavy metals, sulphur and chlorides is legislated and requires considerable laboratory analyses because of the constant variations in feedstock compositions.
In some very specific and rare applications, ULO is cleaned, dewatered, tested and its additive package is topped-off, before the lube oil is used again without leaving the plant site. Again, these applications require extensive laboratory analyses.
There is a need for a viable, safe and flexible process that can destroy the hazardous components in used oil while making products and by-products that are all environmentally friendly.
The re-refining processes alluded to in the previous section aim to recover lubricating oils from the used oil feed streams. There are processes that want to destroy the metal-containing additives in waste oils, and make environmentally acceptable products such as fuels:
Many of these patents propose stationary reactors, operating at atmospheric pressure:
Canadian Patents Nos. 1,309,370 and 2,112,097, and U.S. Pat. Nos. 5,271,808 and 5,795,462 (Shurtleff) disclose an apparatus and a method that are provided reclaiming a useful oil product from waste oil, such as used lubricating oil. The apparatus comprises an oil feed means, a boiler, a heater and a separating means. The heater is used to heat the waste oil in the boiler to a temperature such that heavier hydrocarbons remain unvolatilized, trapping contaminants therewith.
The separating means separates the volatilized lighter hydrocarbons from the unvolatilized heavier hydrocarbons and contaminants.
U.S. Pat. No. 5,871,618 and Canadian Patent No. 2,225,635 (Kong at al.) disclose an apparatus and a process for reclaiming fuel oil from waste oil. The apparatus comprises a thermal cracking unit for cracking the high boiling hydrocarbon material into lighter, lower boiling, material so as to separate hydrocarbon vapor products from viscous materials; a condenser/heat exchanger for condensing the hydrocarbon vapour products to the liquid state; a fuel stabilization unit for chemically treating the condensates so as to give an oil product and solid sediment; and a polishing unit for forming a high quality fuel oil by physically removing solid contaminants. According to the present invention, high quality fuel oil can be obtained together with an environmentally innocuous solid ash cake, through a simple and efficient process.
U.S. Pat. No. 5,362,381 (Brown et al.) discloses a process in which waste lubricating oil is reprocessed into commercially usable diesel fuel and naphtha by thermocracking. A thermocracker unit is fired with sludge removed from the principal pool of oil undergoing vaporization. The vapours are separated from liquids in a primary distillation tower with precisely controlled heating. Resultant vapours are partially condensed. Resultant liquids flow downward through a secondary distillation tower into a reboiler which is heated by a flue gas bypass with an auxiliary burner. Vapours leaving the secondary distillation tower are partially condensed and resultant fluids are passed to a light ends flash tank. Gases from the flash tank fuel the auxiliary burner. Liquids are collected and stored for selling as naphtha. Hot liquids are withdrawn from the reboiler and are immediately cooled to atmospheric conditions. Liquids within specification are stored in a diesel storage tank for further use and sale. Off-specification products are stored in a reflux storage tank and are pumped and heated and sprayed downward in the primary distillation tower for washing the tower and for reprocessing in the thermocracking unit. Some light ends are mixed with sludge in a storage tank. The mixture is pumped as sludge fuel to the burner in a fire tube in the thermocracking unit.
U.S. Pat. No. 5,885,444 (Wansborough et al.) discloses a process for thermally cracking waste motor oil into a diesel fuel product is provided. The thermal cracking process uses low temperature cracking temperatures from 625 to 725 degrees Fahrenheit with ambient pressure to generate a column distilled fraction of diesel fuel mixed with light ends, the light ends being flashed off to produce a high quality #2 diesel fuel. The process further provides for removal from the cracking vessel an additional product stream which, when filtered, is suitable for use as a #3 fuel oil and that can be further blended with a bunker oil to yield a #5 fuel product.
Canadian Patent No. 2,242,742 (Yu) discloses a process and apparatus for the reclaiming and re-refining of waste oils. The process comprises raising a temperature of a feed mixture of fresh waste oil and a recycled non-volatile residue to a range of 400 to 490 degrees Celsius for a time sufficient to cause pyrolysis of the heavy hydrocarbons contained in the feed mixture, but insufficient to permit substantial undesired polymerization, oxidation and dehydrogenation reactions to take place in the feed mixture; cooling the resulting pyrolized waste oil mixture to a temperature in the range of 300 to 425 degrees Celsius, and maintaining the temperature while allowing volatile components in the pyrolyzed waste oil mixture to evaporate, leaving a non-volatile residue containing the contaminants; condensing the evaporated volatile components to form a reclaimed oil product; and mixing the non-volatile residue with fresh waste oil to form more of the feed mixture and repeating the temperature raising, cooling, evaporation and mixing steps on a continuous basis, while continuing to condense volatile components evaporated from the pyrolyzed waste oil mixture. The apparatus comprises a heating unit, a container, a condenser and pumping equipment and piping. The process and apparatus of the present invention generate #2 diesel fuel, gasoline and coke from waste oil. In this patent, the reactor operates under positive pressure.
Among the problems common to stationary reactors in waste oil applications are coking of the reactor walls, which impedes heat transfer from the heat source to the oil to be treated, and fouling of the equipment, not only in the reactor but also upstream and downstream of the reactor.
U.S. Pat. No. 6,589,417 and Canadian Patent No. 2,314,586 (Taciuk et al.) disclose a process by which used oil is treated in a reactor to remove contaminants. The reactor comprises a rotating vessel housed within a heating chamber. The inside of the vessel is indirectly heated by conduction through the vessel walls. The vessel contains a permanently resident charge of non-ablating, coarse granular solids. Within the vessel, the oil is vaporized and pyrolyzed, producing a hydrocarbon vapour. Coke is formed as a by-product. Contaminants, such as metals and halides become associated with the coke. The coarse granular solids scour and comminute the coke to form fine solids. The fine solids are separated from the coarse solids and are removed from the vessel. The hydrocarbon vapours are separated from any fine solids and are routed to a vapour condensation system for producing substantially contaminant-free product oil. The contaminant-rich solids are collected for disposal. This process operates at a negative pressure in the reactor.
Rotating kilns, operating under vacuum, are suggested in processes designed to thermally crack bitumen, heavy oil, rubber tires, oil shale and oil sands, coal or refinery distillation column bottoms.
Canadian Patent No. 1,334,129 (Klaus) discloses an invention that relates to a process and apparatus for the pyrolysis of bitumen. The process involves spraying preheated bitumen into a generally horizontal cylindrical rotating reactor which is heated from the outside and which contains grinding bodies. The bitumen is heated to the pyrolysis temperature and thereby forms a gaseous product and a solid pyrolyzed coke. The solid pyrolyzed coke is removed from the reactor walls by the grinding bodies and the resulting small particles are continuously removed from the reactor through ports in the reactor wall.
EP-A1-0698642 (Hamon et al.) discloses a process by which carbon black is prepared by pyrolysis of rubber waste, pre-ground and freed from Fe, in the presence of steam, CO2, a combustion gas, or a mixt of steam and an inert gas. Pyrolysis is in a rotating oven with indirect heating, with the pyrolysis zone at 600 to 110 degrees Celsius and removal of the prod. at 150 to 350 degrees Celsius. The grain size of the rubber is 2-5 mm. The gas is a mixt. of an inert gas, pref. N2, and steam, with ratio by wt. of water to granulate of 0.1-10, and residence time of 15 seconds to 200 minutes. The steam pressure at the entrance to the pyrolysis zone is 1.33×10-10 Pa, and is made up to atmos. pressure, if the water pressure is not 10 Pa, by dilution with an inert gas (N2, Ar or Kr), by CO2, or by any other gas.
U.S. Pat. No. 4,473,464 (Boyer et al.) discloses a method for producing a distillable hydrocarbonaceous stream and carbonaceous agglomerates from a heavy crude oil by charging the crude oil and finely divided carbonaceous solids to a rotary kiln with the crude oil and carbonaceous solids being charged in a weight ratio from about 0.6 to about 1.5; tumbling the crude oil and finely divided carbonaceous solids in the rotary kiln at a temperature from about 850 degrees Fahrenheit to about 1000 degrees Fahrenheit for up to about 30 minutes to produce a vaporous stream and agglomerate particles containing a residual portion of the crude oil and finely divided carbonaceous solids; separating the agglomerate particles into a product portion of a desired particle size range and a recycle portion; grinding the recycle portion to produce the finely divided carbonaceous solids and heating the finely divided carbonaceous solids prior to recycling the carbonaceous solids to mixture with the crude oil, an improvement comprising: supplying at least a major portion of the heat required in the rotary kiln by heating the crude oil charged to the rotary kiln thereby eliminating the heating of the finely divided carbonaceous solids prior to recycling.
U.S. Pat. No. 4,439,209 (Wilwerding) discloses an apparatus for the continuous non-oxidative thermal decomposition of heat-dissociable organic matter to a solid carbon residue, particularly activated carbon, and a mixture of gaseous products, without substantial coking or tar formation. The apparatus involve a cylindrical rotating drum in a substantially horizontal position, into which feed material is introduced at one end and products recovered at the other end. An axial temperature gradient, increasing in the direction of flow, is maintained within the drum, enabling the exercise of a high degree of control over the reaction to fully convert the feed into the desired products.
Indirectly fired rotating kilns are usually considered inefficient means to convey heat into a reactor. Some propose heating the reactor feed with a hot stream. The hot stream can be circulating gas, liquid or solids.
U.S. Pat. No. 5,423,891 (Taylor) proposes a direct gasification of a high BTU content fuel gas from a hydrocarbon content solid waste material W which may include some glass content is effected by preheating heat carrier solids HCS in a flash calciner to a temperature capable of thermally cracking the hydrocarbon content of the solid waste material W directly into the high BTU content fuel gas. The HCS are separated from the products of combustion and fed into a gas sealed refractory lined horizontal axis rotary kiln retort concurrently with the solid waste W. Momentary contact and mixing of the solid waste W with the HCS in the rotary kiln in the absence of oxygen is sufficient to directly thermally crack the solid waste material into the high BTU gas product. Separated HCS are returned to the flash calciner for reheating. A trommel, coupled directly to the output of the rotary kiln retort and having a trommel screen with mesh openings smaller than glass agglomerates, but sized larger than the HCS, permits separation of the HCS and discharging of glass agglomerates from the downstream end of the trommel screen to prevent shut down of the direct gasification unit. Direct gasification of steel industry waste water treatment plant sludge, automobile shredded refuse ASR, municipal solid waste MSW and refuse derived fuel RDF and oil mill scale is effectively achieved, irrespective of glass content contaminant.
U.S. Pat. No. 4,512,873 (Escher) discloses a process in which the residues obtained in the hydrogenation of oil, especially heavy oil, or of coal are subjected to low temperature carbonization in a drum, preferably a rotary drum, at temperatures between approximately 400 degrees Celsius and approximately 600 degrees Celsius, by means of a carbonization gas after the separation of the condensable portions and heating to temperatures between approximately 600 degrees Celsius and approximately 950 degrees Celsius, which is introduced into the low temperature carbonization drum. The gas is heated to temperatures between approximately 600 degrees Celsius and approximately 950 degrees Celsius indirectly by flue gases arising from the combustion of oil or gas, for example, of excess carbonization gas. The residue to be carbonized at low temperature is introduced into the hot gas in a finely dispersed state and preferably atomized.
From a practical point of view, it is difficult to ensure the integrity of the seals of both the main reactor and the coke incinerator when there is a circulating stream of solids. When produced gas is circulated to heat the reactor feed oil to cracking temperatures, large amounts of circulating gas is required, compared to the fresh feed stream.
There is a need for a flexible and viable process that addresses the drawbacks of existing technologies and that can destroy the harmful components in waste oils while making products and by-products that are useful and environmentally friendly.